System and method to measure series-connected cell voltages using a flying capacitor

Abstract

A system and method for measuring voltage of individual cells connected in series includes a single flying capacitor. The capacitor stores the charge of one of the cells such that an analog-to-digital converter (ADC) connected to the capacitor may process an accurate representation of the voltage of the cell being measured. A plurality of switches electrically connects and disconnects the cells from the capacitor. A controller is in communication with the ADC and the switches for sequencing the switches and recording the voltage measurements of each cell. At least one precision voltage reference device is included to provide the ADC a reference voltage to provide self-calibration.

1. A system for measuring voltage of individual cells in a plurality of cells connected in series, said system comprising:
 a capacitor for storing a charge of at least one of the cells wherein said capacitor includes a pair of terminals; 
 at least one switch electrically connected to said capacitor for selectively connecting at least one of the cells to said capacitor; 
 a plurality of cell switches for electrical connection to the plurality of cells wherein each cell switch includes a first side and a second side with said first side of each cell switch electrically connectable to a positive terminal of one of the cells; 
 a first bus electrically connected to said second side of every other cell switch; 
 a second bus electrically connected to said second side of each cell switch not connected to said first bus; 
 an amplifier for amplifying the charge stored on said capacitor wherein said amplifier includes a pair of inputs electrically connected to said terminals of said capacitor and an output; 
 an analog-to-digital converter (ADC) electrically connectable to said output of said amplifier for converting an amplified analog voltage supplied by said amplifier into digital voltage data; and 
 at least one precision voltage reference (PVR) device for providing a known reference voltage wherein said at least one PVR device is electrically connectable to said capacitor such that the known reference voltage is provided to said capacitor wherein said at least one PVR device is further defined as a first PVR device and a second PVR device and wherein said first PVR device is electrically connectable to said first bus and said second PVR device is electrically connectable to said second bus. 
 
   
   
     2. A system as set forth in  claim 1  further comprising a controller in communication with said ADC for receiving the digital data from said ADC. 
   
   
     3. A system as set forth in  claim 2  further comprising a first PVR switch controlled by said controller and electrically connected to said first PVR device to electrically connect said first PVR device to said first bus. 
   
   
     4. A system as set forth in  claim 3  further comprising a second PVR switch controlled by said controller and electrically connected to said second PVR device to electrically connect said second PVR device to said second bus. 
   
   
     5. A method of measuring voltage of individual cells in a plurality of cells connected in series, said method comprising:
 electrically connecting one of the cells to a capacitor; 
 charging the capacitor for a predetermined charge time; 
 measuring the voltage of the capacitor in response to an elapse of the predetermined charge time to generate a charged voltage reading; 
 discharging the capacitor for a predetermined discharge time; 
 measuring the voltage of the capacitor in response to an elapse of the predetermined discharge time to generate a discharge voltage reading; 
 comparing the discharge voltage reading to a predetermined voltage level; and 
 signaling a malfunction if the discharged voltage reading of the capacitor is greater than the predetermined voltage level. 
 
   
   
     6. A method as set forth in  claim 5  wherein said step of signaling the malfunction is further defined as recording the malfunction to a memory. 
   
   
     7. A method as set forth in  claim 5  wherein said step of signaling the malfunction is further defined as alerting a user of the malfunction. 
   
   
     8. A method as set forth in  claim 5  further comprising the step of electrically disconnecting the cell from the capacitor in response to the elapse of the predetermined charge time. 
   
   
     9. A method as set forth in  claim 5  wherein the capacitor includes a pair of terminals and wherein said step of discharging the capacitor is further defined as electrically connecting the terminals of the capacitor to a ground. 
   
   
     10. A method as set forth in  claim 5  wherein said step of measuring the voltage of the capacitor is further defined as the steps of:
 amplifying the voltage of the capacitor to generate an amplified analog voltage signal; 
 converting the amplified analog voltage signal to a digital voltage signal; and 
 reading the digital voltage signal with a controller. 
 
   
   
     11. A method of measuring voltage of individual cells in a plurality of cells connected in series utilizing a system including a capacitor, an analog-to-digital converter (ADC), and a controller, said method comprising: electrically connecting one of the cells to the capacitor; charging the capacitor for a predetermined charge time; the controller performing ancillary tasks during the predetermined charge time; converting the analog voltage from the capacitor to a digital voltage signal corresponding to the voltage of the capacitor using the ADC in response to an elapse of the predetermined charge time; and reading the digital voltage signal by the controller; wherein said step of the controller performing ancillary tasks during the predetermined charge time is further defined as the controller communicating via a network during the predetermined charge time; wherein the controller communicating via a network is done exclusively during the predetermined charge time.